1. Field of the Invention
The present invention relates generally to an engine cooling apparatus for an automotive vehicle and more specifically to a cooling apparatus provided with a cooling fan to cool an internal combustion engine, for instance, mounted on an automotive vehicle.
2. Description of the Prior Art
In general, it is necessary to cool an engine so that the engine is driven under an appropriate temperature. In cooling the engine, however, the engine must be cooled with due consideration of engine power, fuel consumption rate, engine running noise, etc. To cool the engine, two, water and air, cooling methods are well known. However, the water cooled engines are more widely adopted. In this water cooled engine, the engine is usually provided with a radiator cooled by a motor-driven fan, as disclosed in Japanese Published Unexamined (Kokai) Utility Model Application No. 60-153817, which is incorporated herein by reference.
In this prior-art engine cooling apparatus, however, since the apparatus is so constructed that the operation of the motor driven fan is controlled according to only the coolant temperature of the engine, there exist various problems as follows:
(1) When the engine is being idled (the vehicle halts), in spite of the fact that the engine output power is small and therefore the coolant temperature usually rises very slowly or may not rise in practice, the motor fan is actuated whenever the coolant temperature exceeds a predetermined value, so that the motor fan is noisy although the coolant temperature can be lowered. During engine idling operation, since engine running noise is low, it is not preferable to drive the motor fan from the standpoint of comfortability. Therefore, when a rise in coolant temperature is small, even if the coolant temperature exceeds a predetermined level, it is preferable not to drive the motor fan in order to reduce noise and improve vehicle comfortability.
(2) When the automotive vehicle is travelling at a high speed, since the radiator is cooled sufficiently, it is unnecessary to drive the motor fan according to circumstances. However, in the prior-art apparatus, since the motor fan starts to operate whenever coolant temperature rises beyond a predetermined temperature value, wasteful engine power is consumed and therefore the engine output is reduced, while increasing the fuel consumption rate. In addition, when the motor fan is being driven, since wind blowing against the radiator when the vehicle is travelling (travel wind) is obstructed by the rotating motor fan, another problem arises in that the cooling efficiency is lowered.
The arrangement of the prior-art engine cooling apparatus for an automotive vehicle will be described in further detail hereinafter.